This invention relates to an improved method for the preparation of bis(halophthalimides), monomers useful for the preparation of polyetherimides.
Various types of polyethers, such as polyetherimides, polyethersulfones, polyetherketones, and polyethertherketones, have become important as engineering resins by reason of their excellent properties. These polymers are typically prepared by the reaction of dihydroxyaromatic compounds, such as bisphenol A disodium salt, with dihaloaromatic compounds. For example, polyetherimides are conveniently prepared by the reaction of salts of dihydroxyaromatic compounds with bis(halophthalimides).
U.S. Pat. Nos. 5,229,482 and 5,830,974, disclose the preparation of aromatic polyethers in relatively non-polar solvents, using a phase transfer catalyst which is substantially stable under the polymerization conditions. Solvents disclosed in U.S. Pat. No. 5,229,482 include o-dichlorobenzene, dichlorotoluene, 1,2,4-trichlorobenzene and diphenyl sulfone. U.S. Pat. No. 5,830,974 discloses the use of solvents such as anisole, diphenylether, and phenetole. Solvents of the same type may be used for the preparation of bis(halophthalimide) intermediates for polyetherimides.
In each of U.S. Pat. Nos. 5,229,482 and 5,830,974 the bis(halophthalimide) is introduced into the polymerization reaction as a substantially pure, isolated compound. This process step is often difficult, since solid bis(halophthalimdes) are typically of very low density and fluffy, making weighing and handling burdensome. U.S. Pat. No. 6,235,866 teaches a method of slurry preparation of bis(halophthalimides) by the reaction between diamine compounds and halophthalic anhydride, in equimolar proportions and use of that slurry as such to prepare polyether polymers. But in the disclosed process, considerable caking of the product bis(halophthalimides) occurs, rendering the product difficult to isolate as a pure slurry, resulting in unacceptable levels of residual starting material in the polymer. Also, the presence of water in the resulting product has a deleterious effect on the molecular weight of the polymer. If proper stoichiometric balance between the diamine and the halophthalic anhydride is not maintained, several undesirable by-products remain in the slurry which limit the molecular weight of the polymer, and/or result in polymers with amine end groups Thus there is a need in the art to develop a facile process for the preparation of bis(halophthalimides) having suitable characteristics for conversion to polyetherimide polymers without isolation which overcomes the shortcomings of current synthetic methods.